Material Bi Research Articles

Deformation structuring of aluminum films upon microindentation

The elastic moduli, microhardnesses, and deformation coefficients of aluminum films and bulk materials (Al, Si, Bi, and Ti) are determined using a combination of indentation and atomic force microscopy methods. The surface morphology of aluminum films with a thickness of 10, 200 and 1000 nm on silicon substrates is studied in the initial state and after indentation with loads in the range from 2 to 100 g. The stages of the fragmentation and agglomeration of grains under the influence of loads are revealed experimentally. The effect of the initial grain size, film substructure, and load values on the processes of deformation structuring is determined.

Zn-Sn Electrochemical Cells with Molten Salt Eutectic Electrolytes and Their Potential for Energy Storage Applications

The energy required to run carbon capture systems (CCS) constitutes a huge fraction (30% or more) of that which is produced by coal-fired power plants (1). This parasitic consumption is a major impediment to CCS implementation and retrofitting. The most energy-intensive element of CCS is the reboiler which provides thermal energy for the regeneration of amine-based CO2capture solvents. Our efficiency-boosting method stores excess electrical energy (produced during off-peak hours at baseload power plants) as chemical free energy. This device, resembling a secondary battery, is then optimized to preferentially produce thermal energy in its discharge phase for on-demand, solvent-regenerating heat when required during peak electricity use.We have developed several embodiments of the technology utilizing low cost electrode materials (Zn, Al, Sn, Bi and/or Pb) and molten salt eutectic electrolytes (ZnCl2:KCl, SnCl2:KCl, AlCl3:NaCl:KCl) (2). Figure 1(a) shows heat-generation for a Zn-Zn(Sn) system where a Zn anode is reversibly plated and stripped during charge and discharge, respectively (0 V discharge shown). This uses an air-stable ZnCl2:KCl eutectic electrolyte and molten Sn cathode where Zn reversibly forms an alloy. A ΔT max = 6 °C, steady current density of 10 mA cm-2, and 64% capacity retention after the first cycle demonstrates the proof-of-concept of this novel system which utilizes only ~50 g of earth-abundant active materials in this embodiment. The simple design – one active charge carrying species, Zn2+, in a one-compartment, separator-free cell – has shown promise as a battery technology with other materials, albeit at higher temperatures (3, 4).In an alternate, traditional galvanic cell design, Figure 1(b) demonstrates the temperature dependency of the open circuit voltage (OCV) during cooling (at t=0, cell T= 377 °C and heater is switched off) of a fritted H-cell containing Zn(s)|ZnCl2:KCl(l, eut.)||SnCl2:KCl(l, eut.)|Sn(l) (m.p. = 230, 176, 232 °C). As the molten materials freeze (around 2 h), there is an optimal operating temperature for this binary compartment cell. Interestingly, the OCV is poorer at higher temperatures (an opportunity for energy/cost reduction) and is still high and fluctuating significantly well after all materials are frozen (>3 hours). Ongoing experiments are exploring the mechanism behind this behavior and investigating lower temperature charge/discharge capacities.The thermal energy dissipated upon discharge of these cells can be subsequently captured via heat-transfer fluids (e.g. steam) for injection into the CCS stripper tower. Our studies are fine-tuning the chemistry and engineering necessary to control the balance of heat/electricity generation in these secondary cells; we ultimately envision a molten salt-based hybrid thermal/electrical energy storage medium. It is anticipated from Figure 1(b) that the electrochemical cell can self-heat to desired operating temperatures (achieving molten phase transition) with the excess electricity available during the charging phase.Molten salt electrolytes for electric-to-thermal energy transduction from this study may lead to further progress in niche battery applications since few commercial products of this type operate in the 250-400 °C range.

Engineering of Bi2Se3nanowires by laser cutting

We present a method to control the length and diameter of Bi 2 Se 3 nanowires through laser-cutting. Nanowires of the topologically insulating and thermoelectric material Bi 2 Se 3 were grown using the vapor-liquid-solid method, and cut using a 532-nm-laser operating at a minimum power of 1 μ W. The cutting process can be controlled through laser intensity and exposure time, and is based upon evaporation of Se from the nanowires. This method has many applications from pure research to device engineering.

Synthesis and Characterization of Bismuth Based Novel Inorganic Ion Exchange Materials and Their Analytical Applications.

Two new inorganic ion exchange materials Bismuth(III) antimonotungstate(BiSbW) and Bi(III) iodotungstate(BiIW), salts of heteropoly acids were compared to evaluate their performance as ion exchangers and to explore their efficacy as dye adsorbents. Amorphous BiSbW and BiIW have been synthesized by co- precipitation methods by varying the mixing ratio of the reagents. The most stable samples of BiIW and BiSbW have been characterized for spectral analysis (FTIR), elemental analysis (SEM-EDS), thermal analysis (TGA and DTA) and X- ray diffraction studies. Their ion exchange capacities for Na + ions were found to be 0.85 meqg -1 (BiSbW) and 2.25 meqg -1 (BiIW). The effect on the exchange capacity of drying the exchanger at different temperatures has been studied. The distribution coefficient values shows that these two samples are very selective for Pb 2+ ions. Hence their analytical importance has been established by quantitative separation of Pb 2+ from other metal ions and quantitative removal of Pb 2+ ions from textile industry. The adsorption results

Bridging silicon nanoparticles and thermoelectrics: phenylacetylene functionalization.

Silicon is a promising alternative to current thermoelectric materials (Bi(2)Te(3)). Silicon nanoparticle based materials show especially low thermal conductivities due to their high number of interfaces, which increases the observed phonon scattering. The major obstacle with these materials is maintaining high electrical conductivity. Surface functionalization with phenylacetylene shows an electrical conductivity of 18.1 S m(-1) and Seebeck coefficient of 3228.8 μV K(-1) as well as maintaining a thermal conductivity of 0.1 W K(-1) m(-1). This gives a ZT of 0.6 at 300 K which is significant for a bulk silicon based material and is similar to that of other thermoelectric materials such as Mg(2)Si, PbTe and SiGe alloys.

A concept for a magnetic field detector underpinned by the nonlinear dynamics of coupled multiferroic devices

Multiferroic (MF) composites, in which magnetic and ferroelectric orders coexist, represent a very attractive class of materials with promising applications in areas, such as spintronics, memories, and sensors. One of the most important multiferroics is the perovskite phase of bismuth ferrite, which exhibits weak magnetoelectric properties at room temperature; its properties can be enhanced by doping with other elements such as dysprosium. A recent paper has demonstrated that a thin film of Bi0.7Dy0.3FeO3 shows good magnetoelectric coupling. In separate work it has been shown that a carefully crafted ring connection of N (N odd and N ≥ 3) ferroelectric capacitors yields, past a critical point, nonlinear oscillations that can be exploited for electric (E) field sensing. These two results represent the starting point of our work. In this paper the (electrical) hysteresis, experimentally measured in the MF material Bi0.7Dy0.3FeO3, is characterized with the applied magnetic field (B) taken as a control parameter. This yields a “blueprint” for a magnetic (B) field sensor: a ring-oscillator coupling of N = 3 Sawyer-Tower circuits each underpinned by a mutliferroic element. In this configuration, the changes induced in the ferroelectric behavior by the external or “target” B-field are quantified, thus providing a pathway for very low power and high sensitivity B-field sensing.

Reduction in thermal conductivity of Bi–Te alloys through grain refinement method

Ternary alloys of thermoelectric materials Bi–Sb–Te and Bi–Se–Te of molecular formula, Bi0·5Sb1·5Te3 (p type) and Bi0·36Se0·064Te0·576 (n type), were prepared by mechanical alloying method. The preparation of materials by mechanical alloying method has effectively reduced the thermal conductivity by generating a large number of induced grain boundaries with required degree of disorder. The process of frequent milling was adapted for grain refinement. Substantial reduction in thermal conductivity was achieved due to nano-structuring of these alloys. Thermal conductivity values were found to be very low at room temperature, 0·5 W/mK and 0·8 W/mK, respectively for p and n type materials.

Bismuth(III) dialkyldithiophosphates: Facile single source precursors for the preparation of bismuth sulfide nanorods and bismuth phosphate thin films

Abstract Two different phase pure materials (Bi 2 S 3 and Bi 2 P 4 O 13 ) have been prepared under different conditions using the same single source precursors. Solvothermal decomposition of the complexes, Bi{S 2 P(O R ) 2 } 3 [where, R =Methyl (Me) ( 1 ), Ethyl (Et) ( 2 ), n-Propyl (Pr n ) ( 3 ) and iso-Propyl (Pr i ) ( 4 )] in ethylene glycol gave orthorhombic bismuth sulfide nanorods, whereas aerosol assisted chemical vapor deposition (AACVD) of the same precursors deposited monoclinic bismuth tetraphosphate (Bi 2 P 4 O 13 ) thin films on glass substrates. Surface study of the thin films using SEM illustrated the formation of variety of nanoscale morphologies (spherical-, wire-, pendent-, doughnut- and flower-like) at different temperatures. AFM studies were carried out to evaluate quality of the films in terms of uniformity and roughness. Thin films of average roughness as low as 1.4 nm were deposited using these precursors. Photoluminescence studies of Bi 2 P 4 O 13 thin films were also carried out.

Proximity-effect-induced superconducting phase in the topological insulator Bi2Se3

We have studied the electron transport properties of topological insulator-related material Bi${}_{2}$Se${}_{3}$ near the superconducting Pb-Bi${}_{2}$Se${}_{3}$ interface, and found that a superconducting state is induced over an extended volume in Bi${}_{2}$Se${}_{3}$. This state can carry a Josephson supercurrent, and demonstrates a gaplike structure in the conductance spectra as probed by a normal-metal electrode. The establishment of the gap is not by confining the electrons into a narrow space close to the superconductor-normal metal interface, as previously observed in other systems, but presumably via electron-electron attractive interaction in Bi${}_{2}$Se${}_{3}$.

Transparent thin films of Bi2WO6, Bi4Ti3O12 and Sr0.75Ba0.25Nb2O6

Transparent thin films were prepared by a sol–gel method starting from precursor formation in solution, subsequent spin coating followed by a heating ramp up to a maximum of 700 °C. Starting from a Bi2MoO6 synthesis route, the phase formation and thin film processing of the bismuth containing materials Bi2WO6, Bi3Ti4O12 and additionally of the tungsten–bronze structure Sr0.75Ba0.25Nb2O6 were studied. Spin coating was used to adjust the film thickness in a wide range from 6 to 200 nm. All films were obtained as multicrystalline pure phases according to X-ray diffraction analyses. Scanning electron micrographs revealed homogeneous coatings composed of nanoparticles with a crystallite size varying between 20 and 100 nm, furthermore the UV–VIS spectra demonstrated a high transparency of the films, 80–90% at 600 nm.

Robustness of helical edge states in topological insulators

Topological insulators (TIs) are materials having an energy band gap in the bulk and conducting helical electronic states on the surface. The helical states are protected by time-reversal symmetry and thus are expected to be robust against static disorder scattering. In this work we report an atomistic first principles analysis of disorder scattering in two-probe transport junctions made of three-dimensional TI material Bi${}_{2}$Se${}_{3}$. The robustness of the device against disorder scattering is determined quantitatively. Examining many different scattering configurations, a general trend emerges on how strong is the perturbing potential and how it is spatially distributed so that it can derail the helical states on the Bi${}_{2}$Se${}_{3}$ surfaces.

Proximity effect at superconducting Sn-Bi2Se3interface

We have investigated the conductance spectra of Sn-Bi${}_{2}$Se${}_{3}$ interface junctions down to 250 mK and in different magnetic fields. A number of conductance anomalies were observed below the superconducting transition temperature of Sn, including a small gap that is different from that of Sn, and a zero-bias conductance peak that increases at lower temperatures. We discussed the possible origins of the smaller gap and the zero-bias conductance peak. These phenomena support the idea that a proximity-effect-induced chiral superconducting phase is formed at the interface between the superconducting Sn and the strong spin-orbit coupling material Bi${}_{2}$Se${}_{3}$.

Ground-state properties, excitation spectra, and phase transitions in theS=12andS=32bilayer Heisenberg models on the honeycomb lattice

Motivated by the observation of a disordered spin ground state in the $S=3/2$ material Bi$_3$Mn$_4$O$_{12}$NO$_3$, we study the ground state properties and excitation spectra of the $S=3/2$ (and for comparison $S=1/2$) bilayer Heisenberg model on the honeycomb lattice, with and without frustrating further neighbor interactions. We use series expansions around the N\'eel state to calculate properties of the magnetically ordered phase. Furthermore, series expansions in $1/\lambda=J_1/J_{\perp}$, where $J_1$ is an in-plane exchange constant and $J_\perp$ is the exchange constant between the layers are used to study properties of the spin singlet phase. For the unfrustrated case, our results for the phase transitions are in very good agreement with recent Quantum Monte Carlo studies. We also obtain the excitation spectra in the disordered phase and study the change in the critical $\lambda$ when frustrating exchange interactions are added to the $S=3/2$ system and find a rapid suppression of the ordered phase with frustration. Implications for the material Bi$_3$Mn$_4$O$_{12}$NO$_3$ are discussed.

Néel to dimer transition in spin-Santiferromagnets: Comparing bond operator theory with quantum Monte Carlo simulations for bilayer Heisenberg models

We study the N\'eel to dimer transition driven by interlayer exchange coupling in spin-S Heisenberg antiferromagnets on bilayer square and honeycomb lattices for S=1/2, 1, 3/2. Using exact stochastic series expansion quantum Monte Carlo (QMC) calculations, we find that the critical value of the interlayer coupling, J_{\perp c}[S], increases with increasing S, with clear evidence that the transition is in the O(3) universality class for all S. Using bond operator mean field theory restricted to singlet and triplet states, we find J_{\perp c}[S] ~ S(S+1), in qualitative accord with QMC, but the resulting J_{\perp c} [S] is significantly smaller than the QMC value. For S=1/2, incorporating triplet-triplet interactions within a variational approach yields a critical interlayer coupling which agrees well with QMC. For higher spin, we argue that it is crucial to account for the high energy quintet modes, and show that including these within a perturbative scheme leads to reasonable agreement with QMC results for S=1,3/2. We discuss the broad implications of our results for systems such as the triangular lattice S=1 dimer compound Ba_3Mn_2O_8 and the S=3/2 bilayer honeycomb material Bi_3Mn_4O_{12}(NO_{3}).

Solar hybrid systems with thermoelectric generators

► We examine four hybrid systems with thermoelectric generators (TEGs). ► We studied effect of radiation concentration on the system’s performance. ► Parameters of TEG based on Bi 2 Te 3 were determined and used for analysis. ► TEGs using advanced nanostructured materials were also considered. ► Cost-efficiency estimations and some recommendations for application are made. The possibility of using of thermoelectric generators in solar hybrid systems has been investigated. Four systems were examined, one working without radiation concentration, of the traditional PV/Thermal geometry, but with TEGs between the solar cells and heat extractor, and three other using concentrators, namely: concentrator – TEG − heat extractor, concentrator − PV cell − TEG − heat extractor, and PV cell – concentrator – TEG – heat extractor. The TEGs based on traditional semiconductor material Bi 2 Te 3 and designed for temperature interval of 50–200 °C were studied experimentally. It was found that the TEG’s efficiency has almost linear dependence on the temperature difference Δ T between its plates, reaching 4% at Δ T = 155 °C (hot plate at 200 °C) with 3 W of power generated over the matched load. The temperature dependencies of current and voltage are also linear; accordingly, the power generated has quadratic temperature dependence. The experimental parameters, as well as parameters of two advanced TEGs taken from the literature, were used for estimation of performance of the hybrid systems. The conclusions are drawn in relation to the efficiency at different modes of operation and the cost of hybrid systems, as well as some recommendations in relation to optimal solar cells for applications in these systems.

Bi2(IO4)(IO3)3: A New Potential Infrared Nonlinear Optical Material Containing [IO4]3– Anion

A new potential infrared (IR) nonlinear optical (NLO) material Bi(2)(IO(4))(IO(3))(3) was synthesized by hydrothermal method. Bi(2)(IO(4))(IO(3))(3) crystallizes in the chiral orthorhombic space group P2(1)2(1)2(1) (No. 19) with a = 5.6831(11) Å, b = 12.394(3) Å, and c = 16.849(3) Å. It exhibits a three-dimensional framework through a combination of the IO(3), IO(4), BiO(8), and BiO(9) polyhedra and is the first noncentrosymmetric (NCS) structure containing [IO4](3-) anion. Bi(2)(IO(4))(IO(3))(3) has an IR cutoff wavelength of 12.3 μm and belongs to the type 1 phase-matchable class with a moderately large SHG response of 5 × KDP, which is in good agreement with the theoretical calculations.

First-principles density functional theory study of native point defects in Bi2Te3

We present a first-principles study of the native point defects in the thermoelectric material Bi${}_{2}$Te${}_{3}$. Calculated formation energies of defects and electronic densities of states were analyzed in detail. The most prominent native point defects considered are vacancies and antisite defects on the Bi, Te1, and Te2 sublattices of the Bi${}_{2}$Te${}_{3}$ structure. Vacancies on all three sublattices are found to have much higher formation energies than antisite defects. The most dominant antisite defects are found to be Bi${}_{\mathrm{Te}1}$ at Bi-rich conditions, and Te${}_{\mathrm{Bi}}$ at Te-rich conditions. These lead to the formation of resonant defect states at the top of the valence band and bottom of the conduction band, respectively. Hence they are expected to impact charge and energy transport in a profound way. Furthermore antisite defect pairs tend to form at nearest-neighbor distances, and lead to substantial changes in the electronic structure and hence in the thermoelectric properties of Bi${}_{2}$Te${}_{3}$.

The structure and ionic conductivity of the fluorite-related isostructural materials Bi 20Ca 7NbO 39.5, Bi 10.75Ca 4.375GaO 22 and quenched Bi 9ReO 17

The structure and ionic conductivity of fluorite-related Bi 20Ca 7NbO 39.5, Bi 10.75Ca 4.375GaO 22 and the high temperature form of Bi 9ReO 17, formed by quenching from 800 °C, were studied by neutron powder diffraction, X-ray powder diffraction and impedance spectroscopy. All materials formed distorted δ-Bi 2O 3–related monoclinic superstructures of a fluorite-related hexagonal subcell. The supercell, with P2 1/ m symmetry, is derived from the cubic fluorite subcell axes ( a f, b f, c f) using the transformation matrix: − 1 1 1 0.5 0.5 0 1 − 1 1 . Both Bi 20Ca 7NbO 39.5 and Bi 10.75Ca 4.375GaO 22 are shown to display good oxide ion conductivity (2.52 × 10 − 5 Ω − 1 cm − 1 and 1.02 × 10 − 5 Ω − 1 cm − 1 at 673 K with activation energies of 1.12 eV and 1.25 eV, respectively); quenched Bi 9ReO 17 has enhanced oxide ion conductivity (1.44 × 10 − 3 Ω − 1 cm − 1 at 673 K) with a lower activation energy of 0.76 eV.

In-Plane Transport and Enhanced Thermoelectric Performance in Thin Films of the Topological InsulatorsBi2Te3andBi2Se3

Several small-band-gap semiconductors are now known to protect metallic surface states as a consequence of the topology of the bulk electron wave functions. The known "topological insulators" with this behavior include the important thermoelectric materials Bi₂Te₃ and Bi₂Se₃, whose surfaces are observed in photoemission experiments to have an unusual electronic structure with a single Dirac cone. We study in-plane (i.e., horizontal) transport in thin films made of these materials. The surface states from top and bottom surfaces hybridize, and conventional diffusive transport predicts that the tunable hybridization-induced band gap leads to increased thermoelectric performance at low temperatures. Beyond simple diffusive transport, the conductivity shows a crossover from the spin-orbit-induced antilocalization at a single surface to ordinary localization.

Few-Layer Nanoplates of Bi2Se3 and Bi2Te3 with Highly Tunable Chemical Potential

A topological insulator (TI) represents an unconventional quantum phase of matter with insulating bulk band gap and metallic surface states. Recent theoretical calculations and photoemission spectroscopy measurements show that group V-VI materials Bi(2)Se(3), Bi(2)Te(3), and Sb(2)Te(3) are TIs with a single Dirac cone on the surface. These materials have anisotropic, layered structures, in which five atomic layers are covalently bonded to form a quintuple layer, and quintuple layers interact weakly through van der Waals interaction to form the crystal. A few quintuple layers of these materials are predicted to exhibit interesting surface properties. Different from our previous nanoribbon study, here we report the synthesis and characterizations of ultrathin Bi(2)Te(3) and Bi(2)Se(3) nanoplates with thickness down to 3 nm (3 quintuple layers), via catalyst-free vapor-solid (VS) growth mechanism. Optical images reveal thickness-dependent color and contrast for nanoplates grown on oxidized silicon (300 nm SiO(2)/Si). As a new member of TI nanomaterials, ultrathin TI nanoplates have an extremely large surface-to-volume ratio and can be electrically gated more effectively than the bulk form, potentially enhancing surface state effects in transport measurements. Low-temperature transport measurements of a single nanoplate device, with a high-k dielectric top gate, show decrease in carrier concentration by several times and large tuning of chemical potential.